Well it's not quite a pit bike but here's my street legal Aprilia RS50. In addition being water cooled and having a stock 6spd, she had a 78cc big bore kit, Leo Vinci pipe and 26mm Del'orto carb which let it top out around 70. Oil injection meant filling up at a gas station wasn't a problem. It was a 7/8th scale sport bike so she was only about 230lbs wet I think. The nice slim tires made the flick into corners without hesitation and the factory suspension was great. The last thing it really needed was new rearsets, it would get a little cramped when covering the rear brake. I never did get a chance to take it to the track but those that have said they're an absolute blast. I still miss it.